Project On Acid rain

Acid rain describes any form of precipitation with high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth.

 

Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain falls because of human activities. The biggest culprit is the burning of fossil fuels by coal-burning power plants, factories, and automobiles.

 

When humans burn fossil fuels, sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere. These chemical gases react with water, oxygen, and other substances to form mild solutions of sulfuric and nitric acid. Winds may spread these acidic solutions across the atmosphere and over hundreds of miles. When acid rain reaches Earth, it flows across the surface in runoff water, enters water systems, and sinks into the soil.

 

Acid rain has many ecological effects, but none is greater than its impact on lakes, streams, wetlands, and other aquatic environments. Acid rain makes waters acidic and causes them to absorb the aluminum that makes its way from soil into lakes and streams. This combination makes waters toxic to crayfish, clams, fish, and other aquatic animals.

 

Some species can tolerate acidic waters better than others. However, in an interconnected ecosystem, what impacts some species eventually impacts many more throughout the food chain—including non-aquatic species such as birds.

 

Acid rain also damages forests, especially those at higher elevations. It robs the soil of essential nutrients and releases aluminum in the soil, which makes it hard for trees to take up water. Trees' leaves and needles are also harmed by acids.

 

The effects of acid rain, combined with other environmental stressors, leave trees and plants less able to withstand cold temperatures, insects, and disease. The pollutants may also inhibit trees' ability to reproduce. Some soils are better able to neutralize acids than others. In areas where the soil's "buffering capacity" is low, the harmful effects of acid rain are much greater.

 

The only way to fight acid rain is by curbing the release of the pollutants that cause it. This means burning fewer fossil fuels. Many governments have tried to curb emissions by cleaning up industry smokestacks and promoting alternative fuel sources. These efforts have met with mixed results. But even if acid rain could be stopped today, it would still take many years for its harmful effects to disappear.

 

Individuals can also help prevent acid rain by conserving energy. The less electricity people use in their homes, the fewer chemicals power plants will emit. Vehicles are also major fossil fuel users, so drivers can reduce emissions by using public transportation, carpooling, biking, or simply walking wherever possible.

 

A stand of withered red spruce and Fraser fir trees blights a green vista in North Carolina's Mount Mitchell State Park. The trees fell victim to balsam wooly aphids after being weakened by the effects of acid rain.

 

 

 

Over the years acid deposition, commonly referred to as "acid rain," has rendered dozens of lakes in the Adirondacks uninhabitable for fish and other wildlife. Now, Rensselaer Polytechnic Institute researchers at the Darrin Fresh Water Institute (DFWI) have indicated that some of the most severely affected lakes in that region are showing signs of recovery.

 

"In about half of the 30 lakes under study, an increase in the pH has been observed, a sign that acidic levels are decreasing," says Director Sandra Nierzwicki-Bauer.

 

Levels of nitrogen influenced by nitric oxide, a primary source of acid rain, have decreased moderately in 18 of the 30 lakes the DFWI has monitored since 1994 through its federally funded Adirondack Effects Assessment Program. There also has been an overall reduction of sulfuric acid, another main contributor of acid rain that comes from industry pollutants.

 

The reductions may be correlated with the 1990 Clean Air Act, a federal mandate to significantly reduce emissions that cause acidification, says Nierzwicki-Bauer.

 

More research is needed to pinpoint the exact reasons for the apparent changes seen in the lakes in the southwestern part of the Adirondack Park, an area hardest hit by acid rain.

 

"Recovery doesn't happen overnight," says Charles Boylen, professor of biology and DFWI associate director. "One of the reasons we need long-term data is that other factors can come into play. More or less rainfall in a year, for instance, can lead to a temporary shift in acid-rain levels. You need to track specific data over 10 to 15 years."

 

The DFWI's long-term strategy recently has led to a $2.36 million grant from the Environmental Protection Agency. The five-year grant will allow the DFWI and its collaborators to study acid rain effects in four more lakes in addition to monitoring the other 30. During a workshop in June at the Institute, researchers will announce the most up-to-date results in the acid-rain studies to leading scientists around the country.

 

The Darrin Fresh Water Institute, established more than 25 years ago, has helped increase public awareness concerning the protection of land, water and air. The Institute's all-encompassing study of fresh water systems and ecological processes has earned it high regard in the national scientific community and high marks from the general public.

 

Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological university. The school offers degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of research centers that are characterized by strong industry partnerships. The Institute is especially well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.

 

History

Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides to the atmosphere have increased.[2] [3] In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England.[4] Though acidic rain was discovered in 1852, it was not until the late 1960s that scientists began widely observing and studying the phenomenon. The term "acid rain" was generated in 1972.[5] Canadian Harold Harvey was among the first to research a "dead" lake. Public awareness of acid rain in the U.S increased in the 1970s after the New York Times promulgated reports from the Hubbard Brook Experimental Forest in New Hampshire of the myriad deleterious environmental effects demonstrated to result from it.[6][7]

 

Occasional pH readings in rain and fog water of well below 2.4 (the acidity of vinegar) have been reported in industrialized areas.[2] Industrial acid rain is a substantial problem in Europe, China,[8][9] Russia and areas down-wind from them. These areas all burn sulfur-containing coal to generate heat and electricity.[10] The problem of acid rain not only has increased with population and industrial growth, but has become more widespread. The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation.[11][12] Often deposition occurs a considerable distance downwind of the emissions, with mountainous regions tending to receive the greatest deposition (simply because of their higher rainfall). An example of this effect is the low pH of rain (compared to the local emissions) which falls in Scandinavia.[13]

 

 

[edit] History of Acid Rain in the United States

In 1980, the U.S. Congress passed an Acid Deposition Act. This Act established a 10-year research program under the direction of the National Acidic Precipitation Assessment Program (NAPAP). NAPAP looked at the entire problem. It enlarged a network of monitoring sites to determine how acidic the precipitation actually was, and to determine long term trends, and established a network for dry deposition. It looked at the effects of acid rain and funded research on the effects of acid precipitation on freshwater and terrestrial ecosystems, historical buildings, monuments, and building materials. It also funded extensive studies on atmospheric processes and potential control programs.

 

In 1991, NAPAP provided its first assessment of acid rain in the United States. It reported that 5% of New England Lakes were acidic, with sulfates being the most common problem. They noted that 2% of the lakes could no longer support Brook Trout, and 6% of the lakes were unsuitable for the survival of many species of minnow. Subsequent Reports to Congress have documented chemical changes in soil and freshwater ecosystems, nitrogen saturation, decreases in amounts of nutrients in soil, episodic acidification, regional haze, and damage to historical monuments.

 

Meanwhile, in 1990, the US Congress passed a series of amendments to the Clean Air Act. Title IV of these amendments established a program designed to control emissions of sulfur dioxide and nitrogen oxides. Title IV called for a total reduction of about 10 million tons of SO2 emissions from power plants. It was implemented in two phases. Phase I began in 1995, and limited sulfur dioxide emissions from 110 of the largest power plants to a combined total of 8.7 million tons of sulfur dioxide One power plant in New England (Merrimack) was in Phase I. Four other plants (Newington, Mount Tom, Brayton Point, and Salem Harbor) were added under other provisions of the program. Phase II began in 2000, and affects most of the power plants in the country.

 

During the 1990s, research has continued. On March 10, 2005, EPA issued the Clean Air Interstate Rule (CAIR) . This rule provides states with a solution to the problem of power plant pollution that drifts from one state to another. CAIR will permanently cap emissions of SO2 and NOx in the eastern United States. When fully implemented, CAIR will reduce SO2 emissions in 28 eastern states and the District of Columbia by over 70 percent and NOx emissions by over 60 percent from 2003 levels.[14]

 

 

[edit] Emissions of chemicals leading to acidification

The most important gas which leads to acidification is sulfur dioxide. Emissions of nitrogen oxides which are oxidized to form nitric acid are of increasing importance due to stricter controls on emissions of sulfur containing compounds. 70 Tg(S) per year in the form of SO2 comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires and 7-8 Tg(S) per year from volcanoes.[15]

 

 

[edit] Natural phenomena

The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes and those from biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur containing compounds is dimethyl sulfide.

 

Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.[16]

 

 

[edit] Human activity

 

The coal-fired Gavin Power Plant in Cheshire, OhioThe principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, factories, and motor vehicles. Coal power plants are one of the most polluting. The gases can be carried hundreds of kilometres in the atmosphere before they are converted to acids and deposited. In the past, factories had short funnels to let out smoke, but this caused many problems locally; thus, factories now have taller smoke funnels. However, dispersal from these taller stacks causes pollutants to be carried farther, causing widespread ecological damage.

 

 

[edit] Chemical processes

Combustion of fuels creates sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid.[17]

 

 

[edit] Gas phase chemistry

In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction [4]:

 

SO2 + OH· → HOSO2·

which is followed by:

 

HOSO2· + O2 → HO2· + SO3

In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:

 

SO3 (g) + H2O (l) → H2SO4 (l)

Nitrogen dioxide reacts with OH to form nitric acid:

 

NO2 + OH· → HNO3

 

[edit] Chemistry in cloud droplets

When clouds are present, the loss rate of SO2 is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets.

 

Hydrolysis

Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series of equilibrium reactions:

 

SO2 (g) + H2O  SO2·H2O

SO2·H2O  H+ + HSO3−

HSO3-  H+ + SO32−

Oxidation

There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulfuric acid. The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and manganese in the cloud droplets).

 

For more information see Seinfeld and Pandis (1998).[4]

 

 

[edit] Acid deposition

 

Processes involved in acid deposition (note that only SO2 and NOx play a significant role in acid rain).

[edit] Wet deposition

Wet deposition of acids occurs when any form of precipitation (rain, snow, etc.) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops (see aqueous phase chemistry above) or by the precipitation removing the acids either in clouds or below clouds. Wet removal of both gases and aerosols are both of importance for wet deposition.

 

 

[edit] Dry deposition

Acid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible for as much as 20 to 60% of total acid deposition.[18] This occurs when particles and gases stick to the ground, plants or other surfaces.

 

 

[edit] Adverse effects

 

This chart shows that not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid; for example, frogs can tolerate water that is more acidic (i.e., has a lower pH) than trout.Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life-forms as well as causing damage to buildings and having impacts on human health.

 

 

[edit] Surface waters and aquatic animals

Both the lower pH and higher aluminum concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pHs lower than 5 most fish eggs will not hatch and lower pHs can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.[19] However, the extent to which acid rain contributes directly or indirectly via runoff from the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding watershed) is variable. The United States Environmental Protection Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused acidity in 75 percent of the acidic lakes and about 50 percent of the acidic streams".[19]

 

 

[edit] Soils

Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pHs and are killed.[20] The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins such as aluminium, and leach away essential nutrients and minerals such as magnesium.[21]

 

2 H+ (aq) + Mg2+ (clay)  2 H+ (clay) + Mg2+ (aq)

Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).[22][23]

 

 

[edit] Forests and other vegetation

 

Effect of acid rain on a forest, Jizera Mountains, Czech RepublicAdverse effects may be indirectly related to acid rain, like the acid's effects on soil (see above) or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.

 

Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death.[24][25]

 

 

[edit] Human health

Scientists have suggested direct links to human health.[26] Fine particles, a large fraction of which are formed from the same gases as acid rain (sulfur dioxide and nitrogen dioxide), have been shown to cause illness and premature deaths such as cancer and other diseases.[27] For more information on the health effects of aerosols see particulate health effects.

 

 

[edit] Other adverse effects

 

Effect of acid rain on statuesAcid rain can also cause damage to certain building materials and historical monuments. This results when the sulfuric acid in the rain chemically reacts with the calcium compounds in the stones (limestone, sandstone, marble and granite) to create gypsum, which then flakes off.

 

CaCO3 (s) + H2SO4 (aq)  CaSO4 (aq) + CO2 (g) + H2O (l)

This result is also commonly seen on old gravestones where the acid rain can cause the inscription to become completely illegible. Acid rain also causes an increased rate of oxidation for iron.[28] Visibility is also reduced by sulfate and nitrate aerosols and particles in the atmosphere.[29]

 

 

[edit] Affected areas

Particularly badly affected places around the globe include most of Europe (particularly Scandinavia with many lakes with acidic water containing no life and many trees dead) many parts of the United States (states like New York are very badly affected) and South Western Canada. Other affected areas include the South Eastern coast of China and Taiwan.

 

 

[edit] Potential problem areas in the future

Places like much of South Asia (Indonesia, Malaysia and Thailand), Western South Africa (the country), Southern India and Sri Lanka and even West Africa (countries like Ghana, Togo and Nigeria) could all be prone to acidic rainfall in the future.

 

 

[edit] Prevention methods

 

[edit] Technical solutions

In the United States, many coal-burning power plants use Flue gas desulfurization (FGD) to remove sulfur-containing gases from their stack gases. An example of FGD is the wet scrubber which is commonly used in the U.S. and many other countries. A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulfur dioxide present. The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates.

 

In some areas the sulfates are sold to chemical companies as gypsum when the purity of calcium sulfate is high. In others, they are placed in landfill. However, the effects of acid rain can last for generations, as the effects of pH level change can stimulate the continued leaching of undesirable chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and blocking efforts to restore native life.

 

Automobile emissions control reduces emissions of nitrogen oxides from motor vehicles.

 

 

The term acid rain refers to what scientists call acid deposition.  It is caused by airborne acidic pollutants and has highly destructive results.

Scientists first discovered acid rain in 1852, when the English chemist Robert Agnus invented the term.  From then until now, acid rain has been an issue of intense debate among scientists and policy makers.

Acid rain, one of the most important environmental problems of all, cannot be seen.  The invisible gases that cause acid rain usually come from automobiles or coal-burning power plants.

Acid rain moves easily, affecting locations far beyond those that let out the pollution.  As a result, this global pollution issue causes great debates between countries that fight over polluting each other's environments.

For years, science studied the true causes of acid rain.  Some scientists concluded that human production was primarily responsible, while others cited natural causes as well.  Recently, more intensive research has been done so that countries have the information they need to prevent acid rain and its dangerous effects.

The levels of acid rain vary from region to region.  In Third World nations without pollution restrictions, acid rain tends to be very high.  In Eastern Europe, China, and the Soviet Union, acid rain levels have also risen greatly.  However, because acid rain can move about so easily, the problem is definitely a global one.

 

 

For many years, there was considerable debate and disagreement over what caused acid rain.  Recent scientific work, however, has helped to clarify this

The primary causes of acid rain are sulfur dioxide and nitrogen oxides.  These chemicals are released by certain industrial processes, and as a result, the more industrialized nations of Europe as well as the US suffer severely from acid rain.

Most sulfur dioxide comes from power plants that use coal as their fuel.  These plants emit 100 million tons of sulfur dioxide, 70% of that in the world.

Automobiles produce about half of the world's nitrogen oxide.  As the number of automobiles in use increases, so does the amount of acid rain.  Power plants that burn fossil fuels also contribute significantly to nitrogen oxide emission.

Though human causes are primarily responsible for acid rain, natural causes exist as well.  Fires, volcanic eruptions, bacterial decomposition, and lightening also greatly increase the amount of nitrogen oxide on the planet.  However, even the gigantic explosion of Mt. St. Helens released only about what one coal power plant emits in a year.

Once the tiny pollutant molecules have entered the atmosphere, they can travel for thousands of miles.  Eventually, the particles will combine with other compounds to produce new, often harmful, chemicals.

Acid rain comes down to the earth in the form of rain, snow, hail, fog, frost, or dew.  Once it reaches the ground, the acidity in the substance can harm and even destroy both natural ecosystems and man-made products, such as car finishes.

 

 

Acid rain is having harmful effects both on people and on the natural ecosystems of the world.  Scientists today are convinced that acid rain is severe in many areas, and that it is having an adverse effect on the environments of those locations.

The problem of acid rain is rapidly spreading.  Because it is mainly caused by industrial processes, automobiles, and power plants, those countries that are developed have the most severe acid rain problems.   However, as the undeveloped nations begin to industrialize, acid rain will increase greatly.

Determining just how much the planet is being hurt by acid rain is very difficult because the ecosystems that it affects are so diverse and complex.

Many ecosystems are affected by acid rain.  Bodies of water, such as lakes and rivers, see many of their inhabitants die off due to rising acidity levels.

Acidic water also ruins plant nutrients, hurting plants' ability to survive and to give life to other organisms.

Human-made products are also experiencing degradation from acid rain.  Cars can lose their finishes, and outdoor statues are beginning to rust.

Acid rain's effects are destructive and long lasting.  Though scientists have studied lakes, streams, and many other natural ecosystems to prove its negative effects, acid rain continues to be produced and is increasing in many parts of the world.

 

 

 

Modern science has proven that acid rain is a dangerous and highly destructive problem.  As a result, various ways to limit acid rain have been invented, and some are now being used.

Debate over acid rain and ways of preventing it have raged between environmentalists and corporations.  Businesses such as power companies and car makers oppose controlling acid rain because they fear the effects on their profits.

But in some cases, industries have attempted to curb acid rain production.  The Northern States Power company began working to reduce acid rain in the 1980s, and has invested over a billion dollars to that end.

There are many ways that power plant companies like Northern States can reduce acid rain creation.  They can use coal with a low sulfur content, they can remove the sulfur from smoke their plants release, and they can limit processes known to generate high levels of acid rain.

Policy makers and environmental experts are now looking into the best methods to limit acid rain.

Environmentalists advocate the installation of sulfur cleaning scrubbers in factories, washing sulfur out of coal, and finding new methods of burning coal.  Power plant operators are looking for less expensive solutions to the problem.

Individuals can help by conserving energy or driving their cars less.  Governments can pass laws restricting pollution levels, or can use a variety of methods such as tradable emission permits to reduce acid rain.  Whatever way it is done, acid rain will certainly have to be limited in the future.

 

 

Acid Rain--A Contemporary World Problem

Acid rain is one of the most dangerous and widespread forms of pollution. Sometimes called "the unseen plague," acid rain can go undetected in an area for years. Technically, acid rain is rain that has a larger amount of acid in it than what is normal. The acidity of rain in parts of Europe and North America has dramatically increased over the past few decades. It is now common in many places for rain to be ten to seventy times more acid than unpolluted rain. Many living and non-living systems become harmed and damaged as a result of acid rain. This website gives an informational, in-depth look at acid rain--it's causes and effects; and solutions to the acid rain problem.

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Causes of Acid Rain

Acid rain is caused by smoke and gases that are given off by factories and cars that run on fossil fuels. When these fuels are burned to produce energy, the sulfur that is present in the fuel combines with oxygen and becomes sulfur dioxide; some of the nitrogen in the air becomes nitrogen oxide. These pollutants go into the atmosphere, and become acid.

Sulfur dioxide and nitrogen oxide are produced especially when coal is burnt for fuel. Burning coal produces electricity, and the more electricity that people use, the more coal is burnt. Of course, nowadays people probably couldn't live without electricity, so coal will continue to be burnt; but electricity and energy are constantly being overused. Think of it this way: every time you turn on a light switch or the television set without really needing to, you're indirectly contributing to the acid rain problem. Automobiles produce nitrogen oxides (which cause acid rain), so every time you don't carpool when you can, you are helping to cause acid rain. So now that we know what causes acid rain, here's a look at how acid rain can hurt you and the world around you. . .